Dashpot



Dec. 15, 1964 H. W. BRYANT DASHPOT Filed 001,. l, 1962 INVENTOR y H. W BRYANT ATTORNEY I United States Patent 3,161,261 DASHPQT Ierhert W. Bryant, Middletown, N.J., assignor to Bell Telephone Laboratories, incorporated, New York, N.Y., a corporation of New York Filed Get. 1, 1962, Ser. No. 227,614 4- Qiaims. (61. 188--96} This invention relates to dashpots and particularly to dashpots providing constant damping resistance throughout the strokes of their pistons.

An object of this invention is to provide a constant damping resistance dashpot that because of its novel construction is appreciably reduced in size and weight for any given damping resistance requirement.

Another object of this invention is to provide a corn stant damping resistance dashpot that does not require close tolerances on critical dimensions and thereby has a relatively low manufacturing cost.

These and other objects of this invention are achieved in an illustrative embodiment thereof wherein the dashpot comprises a housing having a piston chamber therein. A protrusion extends into the chamber from one end of the housing and the outside surface of the protrusion is spaced from the inside surface of the housing to define a continuous slot having a resistance portion of uniform cross section and a terminus portion of larger cross section than the resistance portion. A cup shaped piston is movahly positioned in the chamber with the skirt of the piston situated within the resistance portion of the slot throughout the stroke of the piston. Movement of the piston toward the protrusion forces fluid trapped between the piston and the protrusion to flow along the inside surface of the skirt around the edge of the skirt and then along the outside surface of the skirt. A central aperture extends axially through the protrusion and communicates through a plurality of radially extending apertures with the slot to provide a path that shunts the path along the inside surface of the skirt. A plug movably mounted in the central aperture adjusts the amount of fluid flowing through the shunt path.

A feature of this invention resides in a construction that utilizes both the inner and outer surfaces of a cup shaped piston to provide a folded resistance path, thereby decreasing the over-all size and weight of the dashpot.

Another feature of this invention resides in having means for shunting a portion of the resistance path with an adjustable leakage path, thereby providing an adjustment for manufacturing uniformity and reducing the need for close tolerances on critical dimensions.

A complete understanding of the invention and of these and other features and advantages thereby may be gained from consideration of the following detailed description taken in conjunction with the accompanying drawing wherein one embodiment of the invention is illustrated. It is to be expressly understood, however, that the drawing is for the purposes of illustration and description and is not to be construed as defining the limits of the invention.

In the drawing a schematic cross sectional view of the dashpot of this invention is shown.

Referring to the drawing, the dashpot comprises a housing that includes a hollow casing 12 having a piston chamber 14 therewithin. One end of the casing 12 is open, and the inside surface of the casing extending from the open end thereof includes a surface 16 that circumscribes a volume that is uniform in cross section along the length of the surface. Advantagcously the surface 16 is cylindrical. The inside surface of the casing 12 further includes surfaces 13 and 20 on opposite sides of the surface 16 that respectively circumscribe volumes of larger cross section than that circumscribed by the surface 16,

3,161,251 Patented Dec. 15, 1964 the volume circumscribed by the surface 15 being in series with the Volumes circumscribed by the surfaces 18 and 20.

The housing 16 further comprises a closure 22 fastened to the open end of the casing 12', the closure having a protrusion 26 that extends into the chamber 14. The protrusion 26 includes an outside surface 28 that circumscribes a volume, the cross section of which is uniform along the length of the surface 23, the cross section having substantially the same shape as but being smaller than the cross section of the volume circumscribed by the surface 16 of the casing 12. The protrusion 26 also includes an outside surface 30 that is intermediate the surface 28 and the end of the closure 22 closing the chamber 14. The surface 39 circumscribes a volume of smaller cross section than that circumscribed by the surface 28, and the volume circumscribed by the surface 30 is in series With the volume circumscribed by the surface 28.

The surfaces 23 and 3d of the protrusion 26 respectively have the same length as and are in juxtaposition with the surfaces 16 and 21 of the casing 12, and because of the above-recited relationships between these surfaces, they define a continuous slot 32 having a resistance portion 34 of uniform cross section and a terminus portion 36 of greater cross section than and in series with the resistance portion.

The closure 22 has a central aperture 38 extending therethrough that is generally coaxial with the slot 32. The aperture 38 includes a conical portion 40 intermediate the ends thereof that tapers toward the protrusion end of the closure 22, and a plurality of lateral apertures 42 extend laterally from the enlarged end of the conical portion to the terminus portion 3a of the slot 32. A plug 44 is threaded into the end of the closure 22 remote to the protrusion 26, closing that end of the aperture 38, and the plug includes a conical portion 46 that has substantially the same shape as and extends into the conical portion 4% of the aperture. By screwing the plug 44 into or out of the aperture 38, the distance between the conical portion 46 of the plug and the surface defining the conical portion 4% of the aperture is respectively decreased or in creased and the width of the passageway therebetween is thereby decreased or increased.

A cup shaped piston 48 is positioned Within the chamber 14, the piston being secured to a shaft 50 that is supported by a pair of corrugated spring members 52 secured to the casing 12. The spring members 52 are of a stilfness to permit the shaft 50 to move axially but to prevent the shaft from moving transverse to its axis. The piston 48 has a base portion 54 and a skirt portion 56, and it is positioned with the skirt portion thereof situated Within the slot 32. The skirt portion 56, when viewed on end, has substantially the same shape as the resistance portion 34 of the slot 32, and the thickness of the skirt portion is uniform and a little smaller than the width of the resistance portion of the slot. Thus, there are narrow concentric passageways on both sides of the skirt portion 56.

The chamber 14 is filled with a fluid, such as air, and when the piston 43 is moved toward the end of the chamher into which the protrusion 26 extends, the fluid trapped between the base portion 54 of the piston 48 and the end of the protrusion is forced to flow through one of two paths. The first path is through the passageway between the outside surface 28 of the protrusion 26 and the inside surface of the skirt portion 56 of the piston 48, through the passageway between the outside surface 30 of the protrusion and the inside surface of the skirt portion, around the edge of the skirt portion, through the passageway between the outside surface of the skirt portion and the inside surface 29 of the casing 12 and through the passageway between the outside surface of the skirt portion and the inside surface 16 of the casing. This path is a folded 3 one, and it permits a reduction in size and weight of the dashpot. i

The second path is through the protrusion end of the aperture 38, through the passageway between the outside surface of the conical portion 46 of the plug 44 and the inside surface of the closure 22 defining the conical portion 40 of the aperture through the lateral apertures 42, through the passageway between theoutside surface of the skirt portion 56 of the piston 48 and the inside surface 20 of the casing 12, and then through the passageway between the outside surface of the skirt portion and the inside surface 16 of the casing. Of course when the piston 48 is moved in the opposite direction, the fluid also flows through both of these paths in the opposite direction.

The passageways between the outside surface 28 of the protrusion 26 and the inside surface of the skirt portion 56 of the piston 48, between the outside surface of the skirt portion and the inside surface 16 of the casing 12, and between the outside surface of the conical portion 46 of the plug 44 and the inside surface of the closure '22 defining the conical portion 46 of the aperture 38 essentially providethe entire resistance to the flow of the fluid.

This is so because the resistance to. the flow of the fluid is directly proportional to both the circumferential and specified passageways, and therefore the resistance to fluid flowing through the other passageways is negligible.

To provide the desired constant resistance throughout the stroke'of the piston 48, the length of the skirt portion 56 of the piston 43 is greater than the length of the resistance portion 34 of the slot 32 plus the length of the stroke of the piston, the terminus portion 36 of the slot having a length that exceeds the length of the stroke. As a result, part of the skirt portion 56 of the piston 48 extends along the entire length of the resistance portion 34 of the slot 32 throughout the piston stroke, and the length vof the resistance passageways on both sides of the skirt portion thereby remain constant throughout the stroke. In addition, with the spring members 52 directing the movement of the piston 48 generally parallel to the inside surface 16 of the casing 12 and the outside surface 28 of the protrusion 26 and with the width of the resistance portion 34 of the slot 32 being uniform along its length and the thickness of the skirt portion 56 of the piston 48 being uniform along its length, the width of the resistance passageway on both sides of the skirt portion remains substantially constantthroughout the stroke of the piston.

Finally, the dimensions of the resistance passageway between the outside surface of the conical portion 46 of the plug 44 and the inside surface of the closure 22 defining the conical portion 46 of the aperture 38 are fixed by the position of the plug 44 and do not change during the stroke of the piston, and consequently the resistance of this passageway does not change. This resistance passageway, which in efifect shunts the resistance passageway between the outside surface 28 of the protrusion 26 and the inside surface of the skirt portion 56-of the piston 48, provides an adjustment that compensates for variations in dimensions in the other resistance passageways. Thus, a uniform resistance may be obtained from dashpot to dashpot Without necessitating that the critical dimensions thereof be held to closetolerances. The plug 44 is merely screwed in or out to increase or decrease the width of the shunt passageway and thereby increase or decrease the resistance of the dashpot to the desired amount.

What is claimed is:

1. A dashpot comprising:

a housing having a piston chamber therein and a pro-- 4- 1 r trusion extending into the chamber, the protrusion having an outside surface spaced from an inside surface of the housing to define a continuous slot having a resistance portion uniform in cross section throughout its length and a terminus portion of larger cross section than the resistance portion in series with the resistance portion, the protrusion further having a central aperture extending therethrough that isgenerally coaxial with the slot, the central aperture having a contical portion intermediate the ends thereof that tapers toward the chamber end of the protrusion, and a plurality of lateral'apertures extending radially from the central aperture joining the central aperture with the terminus-portion of the 1 slot; V

a plug threaded into the housing end of the central aperture, the plug having a conical portion that has substantially the same shape as and extends into the conical portion of the central aperture; and

a cup shaped piston movably positioned within the chamber, the piston including a base portion and a skirt portion, the skirt portion being uniform in cross section throughout its length, which cross section is substantially the same as but smaller than the cross section of the resistance portion of the slot, the piston being positioned with the skirt portion thereof situated within the resistance portion of the slot throughout the stroke of the piston, the skirt portion being spaced a substantially constant distance from the surfaces defining the slot throughout the stroke, of the piston.

2. A dashpot comprising;

a housing having a piston chamber therein and a protrusion extending into the. chamber, the protrusion having an outside surface spaced from an inside surface of the housing to define a continuous slot having both a resistance portion uniform in cross sectionlthroughout its length and a terminus portion of larger cross section than the resistance portion, the terminus portion being in series with the resistance portion; and

a cup shaped piston movably positioned within the chamber, the piston including a base portion and a skirt portion, the skirt portion being uniform in cross section throughout a portion of its length, which crosssection is smaller than the cross section of the resistance portion of the slot, the skirt portion of uniform cross section occupying the entire length of the resistance portion throughout the stroke of the piston and being spaced from the surfaces defining the slot throughout the stroke of the piston.

3. A dashpot as in claim 2 wherein the outside surface of the protrusion is relieved adjacent to the. base of the protrusion to provide the terminus, portion of the slot.

-4.' A dashpot as in claim 3 wherein the portion of the inside surface of the housing in juxtaposition with the relieved outside surface of the protrusion is also relieved to provide'the terminus portion of the slot.

References Cited in the file of this patent UNITED STATES PATENTS 831,615 Lamrnert Sept. 25, 1906 1,234,311 Duncan f July 24, 1917 1,310,500 Neubert July 22, 1919 1,539,323 Neubert et a1. May 26, 1925 1,576,286 I Lang Mar. 9, 1926 1,584,884 Merrick May 18, 192 2,021,168 Borden Nov. 19, 1935 2,248,865 Griepenstroh July 8, 1941 2,430,760 Daugherty Nov. 11, 1947 1960 Williamson Dec. 20, 

2. A DASHPOT COMPRISING: A HOUSING HAVING A PISTON CHAMBER THEREIN AND A PROTRUSION EXTENDING INTO THE CHAMBER, THE PROTRUSION HAVING AN OUTSIDE SURFACE SPACED FROM AN INSIDE SURFACE OF THE HOUSING TO DEFINE A CONTINUOUS SLOT HAVING BOTH A RESISTANCE PORTION UNIFORM IN CROSS SECTION THROUGHOUT ITS LENGTH AND A TERMINUS PORTION OF LARGER CROSS SECTION THAN THE RESISTANCE PORTION, THE TERMINUS PORTION BEING IN SERIES WITH THE RESISTANCE PORTION; AND A CUP SHAPED PISTON MOVABLY POSITIONED WITHIN THE CHAMBER, THE PISTON INCLUDING A BASE PORTION AND A SKIRT PORTION, THE SKIRT PORTION BEING UNIFORM IN CROSS SECTION THROUGHOUT A PORTION OF ITS LENGTH, WHICH CROSS SECTION IS SMALLER THAN THE CROSS SECTION OF THE RESISTANCE PORTION OF THE SLOT, THE SKIRT PORTION OF UNIFORM CROSS SECTION OCCUPYING THE ENTIRE LENGTH OF THE RESISTANCE PORTION THROUGHOUT THE STROKE OF THE PISTON AND BEING SPACED FROM THE SURFACES DEFINING THE SLOT THROUGHOUT THE STROKE OF THE PISTON. 